Les Houches

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====== Photon studies (isolation, fragmentation, resummation...) for direct photon measurements ======

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still under construction

2nd meeting: Saturday June 6 at 9AM in Auditorium
  * List of presentations and discussion items:
  * Leandro Cieri: Discussion topics, recall of 2013 LH studies and slides (linked to program)
  * Gudrun Heinrich: Recall of 2013 LH studies and plots
  * Ciaran Williams: triphoton and quadriphoton cross sections measurements and isolation comparisons
  * Mauro Chiesa: Isolated photon production in the POWHEG+MiNLO framework: the W \gamma example

Very interesting but timescale not compatible with LH proceedings:
  * Completion of work of Jean-Philippe Guillet (with Catani, Michel Fontannaz and Eric Pilon) in JHEP09(2013)007 (1306.6498) on resumming LL dependence on isol. cone size. Implementation of resummation of ln r terms in JETPHOX for hollow-cone case should enable to compare smooth to hollow-cone and see if the difference is still O(~1%) as shown for solid-cone by Leandro in LH2013 proceedings.

What could be accomplished for the proceedings? (Blackboard discussion)
  * Survey of current/planned isol. criteria used in LHC exps for direct photon measurements
  * to be continued....

References for above presentations (to be completed):
  *Catani Fontannaz Guillet Pilon arXiv:1306.6498 [hep-ph].
  *T. Gehrmann, N. Greiner, and G. Heinrich, Photon isolation effects at NLO in gamma gamma + jet final states in hadronic collisions, JHEP 1306 (2013) 058,arXiv:1303.0824 [hep-ph].


3nd meeting: Tuesday June 9 at 11AM in Auditorium

  * Ciaran Williams: Extension of sigma vs. epsilon plots for smooth vs. fixed cones to smaller epsilon values
  * Preliminary Draft of work plan for the proceedings and discussion:

 
A) Smooth vs. Exp'l Isolation Cone Comparison
   
1) Study additional processes similar to what was done by L. Cieri and D. de Florian for inclusive diphotons in LH2013, see if also obtain agreement within O(1)% for generalisation of LH Photon Isolation Accord."one could define the isolation to be tight enough when the contribution from the fragmentation component does not exceeds ~15−20% of the total cross section" true for all processes?:

--Wgamma (and maybe later Zgamma) with POWHEG+MinLO:  Total cross-section vs Etmax and vs epsilon, and differential in Et_gamma, M_lnu(ll)gamma for 1-2 choices [e.g. epsilon=0.05, cone size](Mauro C. and Fulvio)

--Gamma + jet JETPHOX: Total cross-section vs Etmax and vs epsilon, and differential in Et_gamma for 1-2 choices[e.g. epsilon=0.05, cone size 0.2, 0.4, 0.7? ] (Gudrun H...)

--triphoton (and maybe later quadriphoton) production with MCFM: Total cross-section vs Etmax and vs epsilon, and differential in some variables (Et_gamma 1(2)(3)(4)...)Extend range of epsilon in sigma vs. epsilon plots down to epsilon=0.05 and add scale variations(Ciaran)
   
2) Is unphysical behaviour under 'mismatch' of direct and frag component orders (as reported in LH2013 by Cieri and deFlorian) for gamma gamma, gamma gamma + jet and W/Zgamma also generalized to other processes?

--Gamma + jet with JETPHOX shown June 6 (Gudrun)[yes] (Is it possible to have 'LO fragmention function-LO matrix element' to check?)

--LO fragmentation function possible in time horizon for proceedings (Jean-Philippe, Michel F.)?


B) Fragmentation:  How important is the 'transverse' (or non-collinear) vs. 'longitudinal' (or collinear) fragmentation?
FO calculators (e.g. PHOX family, MCFM, GoSam, ...) only have longitudinal, HO codes with PS (e.g. POWHEG with MiNLO) have both.  While waiting for gamma gamma in POWHEG with MiNLO (probably not for proceedings), use Vgamma (and maybe later Zgamma), MCFM vs. POWHEG + MiNLO, as 'test bench' to evaluate difference in integrated xs, differential observables and comparison with CMS/ATLAS data (Mauro/Fulvio, Ciaran et al, all) 

    
C) Experimental Survey (experimentalists):
  
1) size and character of cones used/planned for use in CMS + ATLAS (size, hollow/solid, Fixed or normalized (epsilon or fixed value)), disc. Frixione?)

2)Survey of direct photon measurements esp Vgamma 

  * Discussion of what to include in a few slides for the summary session tomorrow
Les Houches

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